The present invention concerns the electrical connection of the lead wires of a read/write transducer to a preamplifier circuit formed on a substrate and, more particularly, a method and apparatus for making that electrical connection. The invention involves terminating each of the lead wires onto pads of an intermediate strip, the position of each pad identifying the particular lead wires attached, and subsequently electrically connecting the intermediate strip pads to corresponding leads for the preamplifier circuit.
Typically in magnetic disc drives, signals from a read/write transducer are sent to a preamplifier circuit. The preamplifier circuit is generally located on an electrically insulating substrate. Previous disc drives use conventional coil (thin-film) read/write transducers, wherein the read signal is generated by the change in magnetic flux in a small coil located in the transducer. The transducer is positioned a minute distance above the surface of the recording medium or disc. The change in flux is caused by the motion of the underlying magnetic pattern on the disc surface. The same coil is also utilized by the transducer during the write process on the disc drive.
Generally two lead wires have been used to complete the electrical circuit to and from the terminals of the conventional coil transducer. The two lead wires are utilized to carry the electrical signal both in the read process and the write process, although the read signal is markedly different from the write signal. With a conventional coil transducer, the direction the signal runs (i.e., polarity of the terminals/lead wires) is unimportant, both in the read and the write process. Either lead wire can operate as the positive or negative lead. The two lead wires are not distinct from each other, and can be interchanged with one another without altering the performance of the system. The two lead wires have typically been encased in a single insulative or protective tubing running from the transducer to the pre-amplifier, with no mechanism to distinguish one wire from the other. Connection between the transducer terminals and the pre-amplifier circuit is generally performed by hand alignment and soldering of each transducer lead wire to one of two pads on the preamplifier circuit.
Recently, magneto-resister (MR) transducers have been utilized in disc drives. MR transducers generally continue to perform the write function with a coil in the transducer as described above. However, the MR read function is performed by a separate element in the transducer, a very tiny variable resistor. The variable resistor measures the magnetic flux placed on the resistor current due to the magnetism of the recording medium. Because separate elements are used for read and write functions, the MR transducer requires four terminals/lead wires rather than two. Additionally, in contrast to conventional coil transducers, MR transducers are generally sensitive to the direction or polarity of current flow. A reversal of current flow would disturb the domain alignment within the variable resister element, to the detriment of the MR transducer. Accordingly, the MR terminals/lead wires are designated as positive read, positive write, negative read and negative write, respectively. This polarity of MR transducer leads assures that the direction of current flow is nonreversible and in the direction intended.
The use of MR transducers having four polarized leads has created assembly problems in distinguishing each lead from the others. Wires are normally identified through coloring of the insulation layer surrounding the wire. However, this requires multiple spools of wire which increases the product cost. Additionally, when automation is desired for making the wiring connections, identification of wires through color coding becomes problematic. Not only must the changing operation between various spools of colored wire be automated, but the automated equipment must also have some sort of photo-sensitive eye or other sensing equipment to distinguish between wire colors. Accordingly, a better way to identify and distinguish between the lead wires of MR transducers is desired.
With the advent of MR transducers in disc drives, the read signal strengths have significantly decreased (in comparison to the read signal strengths on traditional coil transducers). To compensate for this lack of signal, low impedance preamps have been employed to improve the noise susceptibility. However, the signal line impedance between the transducer and the preamplifier becomes critical when applying low impedance preamplifiers. The preamplifier circuits for traditional coil transducers have generally been placed on a base board adjacent to the actuator arm. The signal line impedance of this traditional application would result in a significant reduction in band-width for a low impedance preamplifier. A second complication of MR signal line handling is the quantity of signal lines. The addition of two signal lines for MR transducers results in double the density of signal runs between the transducers and the preamplifier over traditional thin film transducer application. This increase in signal density provides a greater propensity for noise between signal lines ("interchannel noise"). To reduce the effects of bandwidth reduction and interchannel noise, it is desired to place the preamplifier as close to the transducers as possible.
In disc drives having MR transducers, the preamplifier assembly has been located on a rotary arm used to selectively position the transducer over the desired information storage track on the magnetic media on the disc. For a 31/2 inch drive, the signal run length from the MR transducer to a pre-amplifier on the actuator arm is about 11/2 to 13/4 inches, saving about 2 inches over placement of the pre-amplifier circuit on a baseboard. However, placement of the pre-amplifier circuit on the actuator arm has made for increasing difficult connection of the transducer leads to the pre-amplifier terminals.
In previous disc drives, the electrical connections between the read/write transducer lead wires and the preamplifier circuit are made by attaching the lead wires to spaced apart interconnection points or terminals on the preamplifier substrate, with the result that the connections are horizontally spaced in a single plane. In so attaching the lead wires, a minimum distance must be maintained between the positions of adjacent interconnection points to prevent shorting.
A problem that has consequently arisen is that the area remaining available on the pre-amplifier substrate for making the interconnection points for electrically connecting the transducer lead wires beyond that needed for the preamplifier circuit is continually decreasing. This is due in part to the use of smaller disc drives with correspondingly smaller rotary arms which have less room for the substrate thereon. Further, the use of increasing numbers of magnetic storage discs in a single disc drive requires a greater number of transducers to be used and therefore increases the number of electrical connections that must be made on the substrate.